Sodium tetrathionate is a salt of sodium and tetrathionate with the molecular formula Na2S4O6. The structure of sodium tetrathionate is somewhat like two sodium thiosulfate (Na2S2O3) molecules joined together at the S+2 ends.

Sodium tetrathionate is formed by the oxidation of sodium thiosulfate (Na2S2O3) with liquid iodine (I2).[1] The sodium tetrathionate Na2S4O6 formed can be isolated from the solution by fractional crystallization.